Distinctive fish tail shocks stem from the
blade trailing edges. These reflect off neighbouring blades and affect the growth
of the trailing edge shear layers further downstream. A lambda shock stems from the
topmost blade. Secondary flows are visible: For instance, horse-shoe vortices rap
around the blades and are marked by thin dark lines running parallel to the shear
layers.

This picture was obtained with a double-pass schlieren method, using a mirrored side
wall and a horizontal knife edge in place of traditional schlieren glass. A 200
microsecond flash was used to freeze the flow.